This invention pertains to novel fibers made of α(1→3) polysaccharides, and a process for their production. The fibers of the invention have “cotton-like” properties but can be produced as continuous filaments on a year-round basis. The fibers are useful in textile applications.
Polysaccharides have been known since the dawn of civilization, primarily in the form of cellulose, a polymer formed from glucose by natural processes via β(1→4) glucoside linkages; see, for example, Applied Fibre Science, F. Happey, Ed., Chapter 8, E. Atkins, Academic Press, New York, 1979. Numerous other polysaccharide polymers are also disclosed therein.
Only cellulose among the many known polysaccharides has achieved commercial prominence as a fiber as a consequence of the many useful products derived therefrom. In particular, cotton, a highly pure form of naturally occurring cellulose, is well-known for its beneficial attributes in textile applications.
It is further known that cellulose exhibits sufficient chain extension and backbone rigidity in solution to form liquid crystalline solutions; see, for example O'Brien, U.S. Pat. No. 4,501,886. The teachings of the art suggest that sufficient polysaccharide chain extension could be achieved only in β(1→4) linked polysaccharides and that any significant deviation from that backbone geometry would lower the molecular aspect ratio below that required for the formation of an ordered phase.
More recently, glucan polymer characterized by α(1→3) glucoside linkages has been isolated by contacting an aqueous solution of sucrose with GtfJ glucosyltransferase isolated from Streptococcus salivarius, Simpson et al., Microbiology, vol 141, pp. 1451–1460 (1995). Highly crystalline, highly oriented, low molecular weight films of α(1→3)-D-glucan have been fabricated for the purposes of x-ray diffraction analysis, Ogawa et al., Fiber Diffraction Methods, 47, pp. 353–362 (1980). In Ogawa, the insoluble glucan polymer is acetylated, the acetylated glucan dissolved to form a 5% solution in chloroform and the solution cast into a film. The film is then subjected to stretching in glycerine at 150° C. which orients the film and stretches it to a length 6.5 times the original length of the solution cast film. After stretching, the film is deacetylated and crystallized by annealing in superheated water at 140° C. in a pressure vessel. It is well-known in the art that exposure of polysaccharides to such a hot aqueous environment results in chain cleavage and loss of molecular weight, with concomitant degradation of mechanical properties. Thus, considerable benefit would accrue to a process which would provide the high orientation and crystallinity desired for fibers without a reduction in molecular weight.
It is highly desirable to discover other polysaccharides having utility as films, fibers or resins because of their widespread importance in the global ecosystem. Polysaccharides based on glucose and glucose itself are particularly important because of their prominent role in photosynthesis and metabolic processes. Cellulose and starch, both based on molecular chains of polyanhydroglucose are the most abundant polymers on earth and are of great commercial importance. Such polymers offer materials that are environmentally benign throughout their entire life cycle and are constructed from renewable energy and raw materials sources.
The properties exhibited by cellulose and starch are determined by the nature of their enchainment pattern. Hence, starch or amylose consisting of α(1→4) linked glucose is not useful for fiber applications because it is swollen or dissolved by water. Alternatively, cellulose, having β(1→4) enchainment, is a good structural material being both crystalline and hydrophobic, and is commonly used for textile applications as cotton fiber. Like other natural fibers, cotton has evolved under constraints, wherein the polysaccharide structure and physical properties have not been optimized for textile uses. In particular, cotton fiber offers short fiber length, limited variation in cross section and fiber fineness and is produced in a highly labor and land intensive process.
Thus, it is desirable to form new structural polysaccharides through processes such as enzymatic synthesis or through genetic modification of microorganisms or plant hosts and fibers made from such new polysaccharides that retain the desirable features of biodegradability, renewable resource-based feedstocks and low cost.